Research moving proxy to NGINX buildpack

[lbeaufort]

Follow-up from #169, WIP PR here: #171, we should move the proxy to NGINX buildpack

**WARNING** overriding nginx.conf is deprecated and highly discouraged, 
as it breaks the functionality of the Staticfile and Staticfile.auth configuration directives. 
Please use the NGINX buildpack available at: https://github.com/cloudfoundry/nginx-buildpack

See research here: #169 (comment) and later discussion

Looks like this repo uses nginx buildpack: https://github.com/cloud-gov/docker-registry-mirror/tree/5fdffe51c6aa3b31bd95e42fc55bc1ed91af409b/proxy. One of the challenges is finding out how to do the syntax for some of the more complex logic we have in the conf file.

Technical consideration

• get cloud.gov research support to understand complexity
• if desired:
  • Move proxy to NGINX buildpack, re-write NGINX conf file
  • Put in follow-up issue for the proxy-redirect app

Completion criteria

• Meet with cloud.gov team to assess upgrading to the new NGINX buildpack
• Implement the changes and see proxy is running on the new buildpack

[lbeaufort]

Moving to 13.11 due to scheduling issues with supplemental support hours